No-till farming practices, also known as conservation tillage or zero tillage, have become common for both row crops and solid seeded crops. No-till farming allows for the growing of crops from year to year without disturbing the soil through tillage. In no-till farming, the soil is left intact and crop residue and standing stubble from the previous year's crop are left to aid in moisture retention, to prevent soil erosion, etc.
In no-till farming it is often desirable to guide seeders, planters, sprayers and the like that are being towed by a work vehicle such as a tractor between the rows standing stubble of the previous year crop. For example, when seeding, it is desirable to plant the seeds between the rows of standing stubble. Thus, specialized equipment has been developed to ensure seeding between rows of standing stubble (see, for example, U.S. Pat. Nos. 4,624,197, 4,616,712 and 6,553,925). As pointed out in U.S. Pat. No. 4,624,197, the advantages of seeding between previous years stubble rows in a no-till cropping system is that it reduces clogging or build up of trash from the previous crop, and reduces wind and water erosion by leaving the old stubble standing.
Many different devices have been used for sensing the stubble or growing plants to send a signal to the towing hitch, allowing it to move left or right so that the towed implement follows the desired path. Ground engaging sensors, such as disclosed in U.S. Pat. Nos. 6,553,925 and 4,616,712, sense the furrows or base of the plant stalks. Other sensors, such as wand sensors as disclosed by U.S. Pat. Nos. 4,930,581, 5,156,219 and 4,821,807 sense the side of the plants or stalks without engaging the ground. However, there are drawbacks with both ground engaging sensors and wand sensors.
There are also times where it is desirable to guide an agricultural implement towed by a work vehicle between rows of growing crops. For example, a guidance system may be beneficial when towing a cultivator to remove weeds, etc. growing between rows of growing crops. Thus, it is important that the cultivator tools are towed through the field of field such that the tools do not engage the crop.
There are several problems that may arise when using ground engaging sensors, in particular in no-till farming. For example, the furrows left by the previous year's seeding operation are often distorted by the weather, i.e., the rains filling them in, or traffic on the field from harvest equipment or spraying equipment. Thus, if the ground engaging sensor is designed to sense the furrows, an uneven furrow may give false readings. Also, ground engaging sensors can be affected stones, clumps of dirt or lumps of straw left by harvesters, etc. so the sensors riding on the ground often give false readings. Thus, often it is necessary to implement a second sensor to give the operator an option as to which sensor is working properly because stubble rows have been trampled by previous field operations (see, for example, U.S. Pat. No. 6,553,925).
Ground engaging sensors are more complex and expensive than a sensor that only engages the crop, as they need to be able to follow the contours of the ground and to be lifted into and out of transport position. They are also subject to damage from rocks and wear. Another disadvantage of ground engaging sensors is that with narrow row spacing cereal crops, it is often desirable to harrow the field after harvest to further spread and break up straw left by the harvesters in order to provide a better seed bed when seeding into wet spring conditions. However, such a harrowing operation fills in the furrows, hence, furrow sensors would not work in a harrowed field.
There are also several problems associated with using wand sensors in no-till conditions. Wand sensors are most often used in growing crops where damage to the plants is a concern. Each of the wand sensors shown in U.S. Pat. Nos. 4,930,581, 5,156,219 and 4,821,807 are wishbone shaped whereby the outer edges are rods designed to engage the crop plants or the previous crop stalks. However, for example, in no-till cereal stubble, the stalks are often 6 to 14 inches high, the row width generally about 2 to 6 inches wide and the space between the rows of stalks generally about 6 to 12 inches. Thus, if the wand gets caught in the middle of the row instead of between the rows it will have a tendency to stay there instead of moving to the desired position between the rows.
Another drawback associated with many of the row sensor devices taught in the prior art arises when these devices are used in narrow row spacing small grains such as Wheat, Barley, or Canola stubble. Because of the narrow row spacing there is potential for the sensor device to get off track for several reasons; rows are knocked down from previous operations, areas of the stubble is lodged and flat on the ground or the moving hitch has moved as far as it can in one direction and cannot go any further. It would be desirable for a sensor device to also provide the operator with the ability to reset the device by centering the towed implement relative to the towing vehicle and starting the guidance system over again.
Thus, it is desirable to have a sensor device that is generally not affected by the contour of the ground or debris on the ground such as stones, straw, etc. and that generally does not get caught in the middle of the stubble row.